Custom catalyst quantifies effect of nanoconfinement

Catalytic materials with nanosized pores and channels play a central role in industrial chemistry. For example, zeolites, a family of nanoporous aluminosilicates, are widely used in petrochemical refining to produce fuels and chemicals. Researchers have long known that confining reagent molecules within nanosized channels of zeolites and other porous materials tends to enhance catalytic reactions. But the complexity of these materials makes it difficult to separate mass transport phenomena from reaction kinetics, which limits basic understanding of these systems. So Wenyu Huang of Iowa State University and Ning Fang of Georgia State University and coworkers designed model catalysts to bypass those difficulties. The materials consist of a solid silica core (100 nm in diameter) decorated with 5-nm-diameter platinum particles; the core is encapsulated within a porous silica shell (120 nm or 80 nm in diameter). The team used those catalysts and a fluorescence microscopy technique that provides single-molecule resolution to track thousands of molecular diffusion and reaction events individually. In the test reaction, a nonfluorescent molecule oxidizes on the platinum particles and forms a highly fluorescent product. By comparing the porous catalysts with nonporous reference catalysts, the team found that nanoconfinement slightly reduces rates of molecular transport, adsorption, and desorption but boosts reaction rates by about a factor of seven, a finding that may aid design of more effective nanoporous catalysts (Nat. Catal. 2018, DOI: 10.1038/s41929-017-0021-1).